There are various tents on the market, most of which are of the enclosed type, which is to cover a structure with a canopy with one side left open for air flow, and the center top portion is supported by four pillars on four corners to raise upwardly at the connecting portion. However, this structure is not strong enough and will be bent inwardly at the top center portion, which collects water when it rains and gains more weight to the tent.
In view of the above shortcoming, this inventor had invented a new design in U.S. Pat. No. 5,638,853, which has the four pillars standing straight, and each pillar has a vertical retractable scissor-like rod thereon, which is connected with each other to form a square shape structure. Each pillar comprises a fixture and a sliding seat adapted to connect with the free end of the scissor-like rod. Each of the fixture and the sliding seat comprises a connecting device to connect a nod rod and a linking rod, the linking rod having one end connected to a sleeve on the nod rod, which is capable of bending towards one direction that forms a cross support to form the tent top. However, this design also comprises some shortcomings, such as:                1. The top is not in arcuate shape, which cannot facilitate draining water and can hardly minimize wind.        2. The retractable rod set has no support.        3. It's not easy to collapse and to expand, and also provides no convenience in storage and carrying.        